1. Field of the Invention
The present invention generally relates to a method and apparatus for transmitting uplink control information in a mobile communication system. More particularly, the present invention relates to a method and apparatus for hopping of a Code Division Multiple Access (CDMA) segment carrying control information in CDMA in an Orthogonal Frequency Division Access (OFDMA) packet data mobile communication system.
2. Description of the Related Art
FIG. 1 is a block diagram of a transmitter 100 for transmitting control information 102 in a conventional OFDMA uplink system. The control information can be a Channel Quality Indicator (CQI), an access probe, or a Multiple-Input Multiple-Output (MIMO) beamforming index.
Referring to FIG. 1, a Walsh code mapper 104 maps the control information 102 to a predetermined Walsh code and a chip repeater 106 repeats the chips of the mapped control information. After I/Q mapping in an I/Q mapper 108, a scrambler 110 scrambles the I/Q-mapped control information. An output A 112 is the result from processing the uplink control information 102 in the components 104 to 110. The output A 112 is transmitted in a method described in FIG. 2.
FIG. 2 illustrates a conventional method for transmitting the output A 112 illustrated in FIG. 1 on a physical channel. That is, after Walsh code mapping, chip repetition, I/Q mapping, and scrambling, the output A 112 is transmitted in the method illustrated in FIG. 2.
Referring to FIG. 2, the vertical axis represents frequency and the horizontal axis represents time. Each smaller rectangle 200 represents a tile. In general, one tile is defined by 16 successive subcarriers and 8 successive OFDMA symbols. The tile definition varies according to system configuration. For example, if a system has 480 available subcarriers, there are 30 tiles, each tile having 16 subcarriers (480=30×16).
The total frequency band of the system is usually divided into a plurality of subbands, as illustrated in FIG. 2. The subbands are used for frequency selective scheduling or other purposes. In FIG. 2, 6 subbands, Subband 0 to Subband 5 exist. Each larger square 202 represents a CDMA control segment. The CDMA control segment includes a plurality of tiles and a plurality of OFDM symbols. The square 202 is called a CDMA segment because the output A 112 is mapped to the square 202, for transmission. The CDMA control segment 202 frequency hops over time as illustrated in FIG. 2 to achieve maximum channel and interference diversity. The CDMA control segment 202 hops on a subband basis. This hopping rule is preferable when the size of the CDMA control segment 202 is equal to that of a subband.
FIG. 3 illustrates a phenomenon that appears when a CDMA control segment hops on a subband basis, in the case where the CDMA control segment differs from a subband in size.
Referring to FIG. 3, it is noted that CDMA control segments are overlapped with one another over a large area along the frequency axis, which is not preferred in terms of maximization of channel and interference diversity. In general, the CDMA control segment size is determined by the size of the control information 102 and the subband size is determined by a frequency selective scheduling gain. Therefore, the CDMA control segment size is different from the subband size.